1. Field of the Invention
The present invention relates to a method of chucking a semiconductor wafer on a hard surface to polish one side of the wafer.
2. Description of the Prior Art
Conventionally, it is generally known that a semiconductor wafer is attached on a hard surface with appropriate tacky wax therebetween when the wafer is polished into a so-called mirror wafer. In such a method, however, it is difficult to obtain desirable mirror wafers because of nonuniformity in the thickness of the wax or similar reasons. Therefore, flatness precision on the semiconductor wafer per se must be limited. This method also requires washing after the polishing process to remove the wax from the back of the semiconductor wafer, so that the semiconductor wafers to be processed by this method are likely to be contaminated with the residual wax or damaged by handling during washing.
There have been heretofore proposed many methods which do not use such tacky wax. As one of such methods, there is known a method in which a special organic material such as polyurethane or similar like material is inserted between the semiconductor wafer and the hard surface as a cushion material (Japanese Patent Laid-Open Publication No.62-297064). In this method, however, it is difficult to desirably control the precisions in shape including flatness and parallelism after the polishing process to the wafer surface.
Also, there is known a method in which the semiconductor wafer is held on the hard surface by vacuum chucking through fine holes formed in the surface. However, in this method, since the semiconductor wafer directly contacts with the hard surface, the shape precisions including flatness and parallelism tend to be deteriorated by unevenness of the backside surface of the wafer, sandwiched fine particulate dust or the vacuum-chucking holes.
In an effort to alleviate such harmful effects as the unevenness of the back surface of the wafer or sandwiched particulate dust, there is disclosed a method of chucking the semiconductor wafer on a hard surface by surface adhesion of silicone rubber (Japanese Patent Laid-Open Publication No. 62-111442). In this method, however, the semiconductor wafer is chucked with conventional silicone rubber whose surface adhesion to the wafer is not sufficient. The semiconductor wafer tends to move in the planar direction thereof during the mirror polishing process. The polishing precision of the semiconductor wafer is undesirably dependent upon the flatness of the silicone rubber surface.